Oxide semiconductor materials which are intensively studied comprise IGZO (indium gallium zinc oxide), ITZO (indium tin zinc oxide) and the like. In such oxides materials, there are a lot of oxygen vacancy defect states containing two electrons therein. When these oxides in the thin film transistor (TFT) are irradiated by light, electrons in the oxygen vacancies are excited to have a transition to the vicinity of the conduction band of the oxide materials. When the light irradiation is removed, the returning speed of photo-generated electrons caused by oxygen vacancies to the ground state is slow, resulting in a large leakage current of TFT and a poor light stability of TFT.
At present, light-shielding organic materials, such as resin, BM (Black Matrix), CF (Color Filter) and the like, are commonly used in the industry for shielding oxide TFT (mainly the portion of the active layer) from light, which reduces intensity of the light irradiated onto the TFT and thus the influence on TFT characteristics by light irradiation. As illustrated in FIG. 1, a light-shielding layer for shielding TFT is made of resin material and reduces intensity of the light irradiated onto the TFT, so that the influence on oxide TFT characteristics by light irradiation can be improved.
However, the above method of shielding TFT by organic material is only applicable to a circumstance in which a light source irradiates from the top of the TFT. When the TFT has a bottom gate or top gate structure and light is incident onto the bottom of TFT, i.e., the light source irradiates TFT through the substrate, as illustrated in FIG. 2 and FIG. 3, the aforementioned organic material cannot shield the TFT from light irradiation and the channel region of the active layer is still irradiated by light, thus resulting in a large leakage current in TFT.